1. Field of the Invention
The present invention relates to a data transmission apparatus and a method for transmitting data, and in particular, to a data transmission apparatus for transmitting digital video and audio data between respective audio visual apparatuses, such as a digital video cassette recorder (referred to as a digital VCR) or the like, and a method therefor.
2. Description of the Related Art
There has been currently under development of digital VCRs for recording video and audio in a form of digital signals expressed by 0s and 1s, respectively, for the purpose of achieving high-quality video and audio. One of major features of the digital VCRs is that the qualities of video and audio signals are not deteriorated through dubbing these signals. In the digital VCR, an audio signal, a video signal and the other control signal or the like are recorded in a form of digital signals on a magnetic tape, respectively.
Since transmission of data is executed in a form of a digital signal between the digital VCRs, the transmitted data does not change in the transmission stage. Therefore, the recorded data can be transmitted as it is from an audio visual apparatus to another audio visual apparatus.
In particular, in a digital VCR for consumer use, the video signal is recorded onto the magnetic tape in a form of a compressed video signal so that the amount of data to be recorded thereonto can be reduced for the purpose of reducing the amount of consumption of the magnetic tape. In order to transmit a video signal reproduced by a digital VCR therefrom to another digital VCR in a form of an analog signal and to record the transmitted video signal in the latter VCR, the reproduced video signal is decompressed so as to be converted into an analog video signal. The analog video signal is inputted to the digital VCR in which the video signal is to be recorded. In the digital VCR, the analog video signal is converted into a digital video signal so as to be compressed again. Through the above-mentioned compression and decompression processes, the quality of the image of the video signal may deteriorate.
In the case when transmitting the video signal in a form of a compressed digital signal, there is a great advantageous effect of causing no deterioration of the quality of the image thereof due to the transmission process because the compression and decompression processes are not required.
For the digital VCR is defined a digital interface for transmitting video and audio signals in a form of digital signals. In the digital VCR, one track is segmented into a plurality of sectors, and then a subcode for the video and audio signals, time code, and the like are recorded in respective sectors. In a general digital interface, data to be recorded in the sectors are transmitted in a predetermined order.
The first problem to be solved by the present invention is as follows. When one field is a transmission unit, the period of one field is greatly different between the television broadcasting system having a frame frequency of 25 Hz such as SECAM system, PAL system or the like and another television broadcasting system having a frame frequency of 30 Hz such as NTSC system. Therefore, a time interval required for transmitting one transmission unit is greatly different depending on the television broadcasting system.
When transmitting data of a plurality of television broadcasting systems by means of an identical transmission medium between a plurality of audio visual apparatuses such as digital VCRs or the like, there is such a problem that the time interval for transmitting one transmission data unit is required to cope with a plurality of types of the transmission time.
The second problem to be solved by the present invention is as follows. In the case of implementing a digital VCR for consumer use, it may be required to transmit video and audio signals of both of the high-definition television (HDTV) broadcasting system such as High-Vision system or the like and the current television broadcasting system such as NTSC system or the like between a plurality of digital VCRs or the like. In order to achieve cost reduction, it is required to provide an identical transmission path line in both of the case where the signals of the current television broadcasting system are transmitted and the case where the signals of the high-definition television broadcasting system are transmitted. However, the amount of information of the video signal of the high-definition television broadcasting system is much greater than that of the current television broadcasting system. Since the amount of data is greatly different between the signals of the high-definition television broadcasting system and the signals of the current television broadcasting system, there is such a problem that data of the signals of the current television broadcasting system and the data of the signals of the high-definition television broadcasting system are compelled to be transmitted in different manners.
The third problem to be solved by the present invention is as follows. Since any conventional digital VTR copes with only the standard television signal such as an NTSC television signal, a SECAM television signal, a PAL television signal or the like, then the other type of inputted signal cannot be recorded in the conventional digital VTR. On the other hand, in order to increase the number of types of signals which can be inputted and recorded onto a magnetic tape, there has been suggested a method of changing either the number of sectors or the structure of sectors in each track. In this case, not only a track structure flag representing the number, arrangement and the like of sectors in a track, but also a sector structure flag representing, for each sector represented by the track structure flag, the structure of the sector are to be recorded within the track on the magnetic tape.
However, the conventional digital interface has such a problem that it cannot cope with the change of such track structure as described above since it communicates with other apparatuses always in a previously fixed format. Furthermore, since all the data including the other sectors are required to be transmitted even in the case where the data of a specified sector is desired to be transmitted, there is such a problem that the excessive transmission band for unnecessary transmission must be provided.
The fourth problem to be solved by the present invention is as follows. In the digital VCR, other than the video and audio signals, not only VAUX (Video Auxiliary) data representing the type, kind or the like of the television broadcasting system of the video signal, but also AAUX (Audio Auxiliary) data representing the sampling frequency or the like of the audio signal are additionally recorded onto the magnetic tape. The above-mentioned these information data are very important data necessary in reproducing the recorded video and audio signals in the reproduction stage. Therefore, the information data are repetitively recorded a plural of times in one frame period of the video signal. In transmitting the video and audio signals from the digital VCR to another digital VCR, the VAUX and AAUX data corresponding to the video and audio signals must be additionally transmitted thereto. In general, the data are transmitted a plurality of times in one frame period in conformity with the recorded tracks.
However, in a bad reproducing condition, the probability of occurrence of the phenomenon becomes higher that an error correcting process is executed by an error correcting function, wherein the phenomenon is referred to as an "error correction" hereinafter). Since the error-corrected data does not allow its error to be detected any more, then the error data is transmitted as it is. When there is no error or when an error has occurred and then appropriately corrected, the identical VAUX and AAUX data are transmitted a plurality of times in one frame period, and therefore, the proper process is required to be executed in response to the received data on the receiver side.
However, when the error correction is performed, there is such a possibility that different VAUX and AAUX data or the like are transmitted in one frame period. In such a case, it is impossible to discriminate which VAUX and AAUX data are correct on the receiver side, and then this results in such a problem that the television broadcasting system can not be correctly selected, and the sampling frequency can not be correctly set.